Problem: $ C = \left[\begin{array}{rrr}2 & 1 & -2 \\ 3 & -2 & -1 \\ 4 & 2 & 0\end{array}\right]$ What are the dimensions of matrix $ C$ ?
The first dimension is the number of rows in the matrix. How many rows does $ C$ have? The second dimension is the number of columns in the matrix. How many columns does $ C$ have? So, $ C$ is a 3 $\times$ 3 matrix.